Capacity balance circuit



April 20, 1937. SHEPARD, JR 2,077,592

CAPACITY BALANCE CIRCUIT Filed Feb. 1, 1935 29 3 2 3; 31 -L -L- our/w /aA. c.

INVENTOR. FRANCIS H. SHEPARD JR.

1%. QWV

ATTORNEY.

Patented Apr. 20, 1937 UNITE STATS OFICE FATE CAPACITY BALANCE CIRCUITporation of Delaware Application February 1 Claim.

The present invention relates to a capacity divider circuit andamplifier and more particularly to a capacity operated relay or powerdevice in which a capacity divider is arranged to supply alternatingcurrent to the grid of a thermionic amplifier in such a way that thealternating current potential is in phase or 180 out of phase with thealternating current potential supplied to the anode of the thermionicamplifier.

It is an object of the present invention to devise a capacity operatedrelay or power device in which a capacity divider and an alternatingcurrent operated direct current amplifier are connected to a commonalternating current power supply in such a manner that variations of thealternating current output of the capacity divider due to the conditionof adjustment of the capacity divider is applied to the grid of theamplifier in such a manner as to cause the direct current output of theamplifier to rise or fall with the condition of the capacity ratio.

In many cases, as for instance, burglar alarms and temperature controldevices it is very desirable to have an arrangement which willefiiciently amplify small capacity changes.

The present invention may be broadly stated to comprise a method andmeans for operating a capacity bridge circuit on commercially availablealternating current in order to de- 30 tect small changes in capacityand in accordance with these small changes control a considerable amountof power, in, say, the plate circuit of a power tube. In accordance withthe W present invention it is possible to control, for

" instance, the temperature of a furnace by means of small changes inthe capacity of a small condenser plate placed near the needle of asensitive temperature indicating meter. This capacity change is utilizedto operate an amplifier which may include a power tube, the output ofthe power tube being operatively associated with a suitabie solenoid orsimilar device to drive a balanced valve used to control the gas fed to45 the furnace and hence the temperature of the furnace.

It is an object of the present invention to produce a device which isextremely sensitive, simple, stable, positive in operation and low incost.

The various broad aspects of the invention are illustrated by thecircuit diagrams in the accompanying drawing wherein,

Figure 1 is a circuit diagram illustrating a 55 preferred form of theinvention showing a ca- 1, 1935, Serial No. 4,470

pacity bridge circuit in conjunction with an a. c. operated d. c.amplifier; and,

Figure 2 is a circuit diagram. of a modified form of the invention.

Referring to Figure 1 terminals i and 2 of transformer 3 are arranged soas to be connected to a suitable power supply line, as for instance, theusual 120 volt 60 cycle commercially available power lines. Thetransformer 3 includes a primary 4 and two secondaries 5 and 'l. Adouble triode tube ll having two plates is and two grids I9 and 22 andtwo indirectly heated cathodes 23 and 2| has its two plates 28 and 23connected to one end of the secondary 5 through the medium of condensersI4 and I5 respectively and the conductor It. The cathodes 2c and El arepreferably connected together and through the medium of a conductor 27both thereof are connected to the center tap of the secondary 5.

cross the secondary 5 there are connected two variable condensers 9 andit in series. Point H which is common to the two variable condensers 9and It] is connected directly to the grid I3 of tube l1 and also throughthe medium of two resistors H and I2 to the anode 13. A connection isprovided between a point common to the resistors H and i2 and theconductor 21 which connection includes a resistor l3.

Plate I8 is also connected to the conductor 2'! by a circuit whichincludes resistor 29, resistor til and a condenser 3| all in series inthe order mentioned. A point of the last-named circuit which isintermediate the resistors 29 and 3t is connected to the grid 22 of thetube il. By means of a resistor 32 the anode 23 is connected to theconductor 2'1. A connection between anode 23 to the center tap of thesecondary 5 includes a resistor 33, a resistor 34, a condenser 35 andconductor 21 all in series.

A tube 36 shown as having an anode, a cathode and a grid may be utilizedas an amplifier, the grid of this tube being connected to a pointintermediate the resistors 33 and 3 3 as shown. The anode of tube 36connects to an output terminal 3?, the other output terminal 38 beingconnected by means of the conductor S6 to the upper portion of thesecondary 5.

In order to heat the cathodes 20 and 2| of tube l1 and the cathode oftube 36 there is provided a heating circuit which includes the secondary1, a heater circuit 24 connected across the secondary I through themedium of conductors 39 and 40 and the leads 25 and 26 which feedcurrent from the secondary 1 to the heating circuit for the cathode oftube 36. The mid-point 8 of the secondary l is connected to the centertap of secondary 5 which if desired may be grounded.

In Figure 2 it is obvious that the circuit arrangement is similar tothat shown in Figure 1 except that the resistor I2 is connected betweenanode Id of tube I7 and the center tap of secondary 5 through lead 21,it being noted that resistors It and I3 are eliminated.

It is to be understood that either of the variable condensers 9 and I0may represent the variable element of any sensitive indicating ormeasuring device such as the capacity of a meter needle to a smallcondenser plate or element, the capacity between condenser elementsmounted on any two objects movable with respect to each other or thecapacity between any two fixed condenser elements the capacity betweenwhich may be varied by a 3rd element brought near or between thecapacity elements. The 3rd element may be conductive or may be ofdielectric material.

In operation, variable condenser 9 may be utilized to balance thecircuit or bridge. When condensers 9 and II] are balanced the a. c.potential on the grid I9 is such that the average d. c. drawn by anodeI8 has a value which is sufiicient to cause the anode I8 to assume amean d. c. potential by virtue of the I. R. drop in resistors i2 and E3in the case of Figure 1, and resistor 52 alone in the case of Figure 2,to supply the desired d. c. bias to grid 22. In Figure 1 the d. 0.potential of the grid I9 is obtained by connecting to the commonconnection between resistors I2 and I3 through the filter resistor I I.The potential of this common connection is proportional to the d. 0.potential of the anode I8 by the ratio of the value of resistance I3 tothe value of resister I 2 plus resistor I3. In this manner the firsttriode section of tube I1 is self-biased.

In the case of Figure 2, the grid I9 assumes an average (1. 0. potentialwhich is equal to the peak positive alternating current voltage appliedbetween grid I9 and cathode 20 as determined by the voltage of secondary5 divided by the fraction which is given by the value of condenser I0over the value of condenser 9 plus condenser I0. Any excessive grid (1.0. potential on the grid I9 will leak off because of the normal currentsof the negative grid.

In the above discussions it is to be distinctly understood that in orderto simplify the description the effects of the tube capacities have beenconsidered negligible. However, it is appreciated that these tubecapacities are not negligible and in fact should be taken into accountin designing various commercial apparatus in accordance with the presentinvention.

Taking the case of temperature control devices, let it be supposed thatdue to a change in temperature the capacity value of the condenser I0 isreduced. In such a case the grid I9 will swing more positive in phasewith the supply Voltage applied to the plate I8. This causes the platecurrent to increase. In case the capacity value of the condenser II]should increase then the grid I9 will swing less positive than formerlywith the result that a reduction of plate current occurs. These changescause an increasing or decreasing potential on the plate I8. Theremaining portion of the circuit including the second section of thetube I! and the tube 36 comprises an a. c. operated d. c. amplifier suchas disclosed in a copending application Serial Number 727,968 filed May28, 1934, entitled Amplifier circuits. The amplifier circuit is utilizedto amplify the potential variations described above.

In a particular actual embodiment of the invention it was found thattube I I could be a type 53 or a type 79 tube while tube 36 could be atype 56 or a type 2A3 tube. In this actual circuit arrangement, theresistors II and I2 were, respectively, five megohms, and two megohmswhile resistor I3 had a value of 0.1 megohm. Condensers I4 and I5 eachhad a value of 0.1 Mid. and the values of resistors 29 and 3!] were,respectively, two megohms and 0.15 megohm, While the values of resistors32, and 33 were two megohms each and resistor 34 one megohm. It wasfound that condensers 3| and 35 could be iven the values 0.1 Mfd. forexcellent results.

While there have been disclosed only two modifications of the inventionit is to be distinctly understood that the principles underlying the in-Vention may be carried out in many other forms without departing fromthe spirit of the invention and no limitations upon the invention areintended other than those imposed by the scope of the appended claim.

What I claim is:

In a capacity operated relay or power device, a source of alternatingcurrent energy, a capacity divider connected across the source, saiddivider comprising a pair of condensers, a thermionic amplifierincluding a space discharge device provided with an anode, a cathode anda grid electrode, means connecting the space path of said device to thesource to thereby impress an alternating current potential upon theanode of the device, means for connecting the grid electrode of thespace discharge device to a point of the capacity divider at which theratio of the alternating current potential which is thereby impressedupon the grid and the alternating current potential impressed upon theanode is real, a path including resistance means connected between theanode and cathode of the discharge device, and means comprising aconnection between the grid electrode and a point of said path forbiasing the grid electrode, said condensers being proportioned withrespect to each other, and the capacity divider as a whole so that thealternating current potential impressed upon the grid is such that theaverage direct current drawn by th anode has a value which is sufiicientto cause the anode to assume a mean direct current potential relative tothe cathode by virtue of the drop in the said resistance means, anoutput circuit for the space discharge device and a utilizing circuitconnected to the output circuit. FRANCIS H. SHEPARD, JR.

